Note: this site last updated in 2006
Cellular proteins are incorporated into HIV particles
An article from "The Molecules of HIV" (c) Dan Stowell
Most of the work on HIV so far has considered HIV's "own" proteins. This is understandable; but did you know that when a HIV particle buds off from a host cell, it also takes lots of proteins with it from the host cell?
The most common inclusion is HLA protein, which is cell-surface protein involved in the human immune system. There are various varieties of HLA produced by cells in the human body, but most commonly, HIV incorporates HLA-DR.
It's often hard for researchers to tell, if they find a cellular protein in HIV particles, whether it's there "on purpose" or "by accident". But the quantities of HLA-DR are too large for it to be an accident, so something must be going on here. Why would HIV drag other proteins into the budding virus particle? Does it mean that these other proteins are important to the mechanism of HIV infection?
The answer, for HLA-DR at least, seems to be yes. Viruses with no HLA-DR are slightly less infectious; and there's evidence that the HLA-DR also affects how deadly the virus is to T-cells.
HLA-DR is a cell-surface protein, so it acts like a cell-surface protein in HIV, sticking out of the lipid bilayer just like the env spikes do. Other cell-surface proteins that have been found incorporated into HIV include HLA class I, and various cell adhesion proteins (proteins which help cells stick to each other).